PIXE AND EMP ANALYSES OF VOLCANITES FROM NEA KAMENI ISLAND (AEGEAN SEA, GREECE)

The major and trace element compositions of several minerals and their surrounding groundmass in the volcanic rocks from the post-caldera Ne a-Kameni island of the Santorini volcanic complex, Aegean Sea, have be en determined, in-situ with particle-induced X-ray emission (PIXE) and wavelength dispersive X-ray analysis with an electron microprobe (EMP ). The lavas are typically calc-alkaline dacites. All samples are porp hyritic with a phenocryst mineralogy dominated by plagioclase, augite, hyperstene and Ti-magnetite. The phenocrysts range in size from 200 m um to 2.5 mm. The PIXE and EMP analyses were done on sections polished with diamond paste. They were sufficiently thick (almost-equal-to 100 mum) to stop the 2.7 MeV protons used for the analysis and yet thin e nough for individual minerals to be seen with transmitted light. The s pecific minerals and groundmass areas to be analyzed had been selected and marked through conventional microscopic examination prior to anal ysis. Solid/liquid partition coefficients, which depend much less sign ificantly on the method for determining the concentrations, were calcu lated from the element abundances in phenocrysts and corresponding gro undmass.